Effect of chemical substitution on the Neacuteel temperature of multiferroic Bi1-xCaxFeO3

Multiferroic BiFeO3 ceramics have been doped with Ca and it is found that the magnetic Neel temperature (T-Neacuteel) increases as Ca concentration increases, at a rate of 0.66 K per 1% Ca (molar). The smaller ionic size of Ca compared with Bi results in a contraction of the lattice, suggesting that Ca doping can be regarded as a proxy for hydrostatic pressure, with an equivalence of 1% Ca=0.3 GPa. Combining these results, we argue that hydrostatic pressure should increase the magnetic transition temperature of BiFeO3 at a rate around partial derivative T-N/partial derivative P similar to 2.2 K/GPa. Our results also suggest that pressure (chemical or hydrostatic) may be used to bring the ferroelectric critical temperature T-c and the magnetic T-Neacuteel closer together, thereby enhancing magnetoelectric coupling, provided that electrical conductivity can be kept sufficiently low.